In response to higher operating speed of semiconductor devices and miniaturization of wiring patterns, copper having higher conductivity and electromigration resistance than aluminum now draws attention as a wiring material
As a method of forming a Cu film, there has been known CVD (chemical vapor deposition) processes that deposit a Cu film on a substrate through a thermal decomposition reaction of a source material gas containing Cu or a reduction reaction of a source material gas containing Cu. Cu films formed by the CDV processes show excellent coverage performance and excellent performance of filling up fine and deep patterns, and therefore can advantageously be used for forming fine wiring patterns.
As one of CVD processes, there has been known an ALD (Atomic Layer Deposition) process capable of forming a Cu film with excellent quality. In the ALD process, a Cu film with a desired thickness is obtained by repeating a step of adsorbing a source material gas to a base layer with a thickness of a molecular (atomic) layer level, and a step of reacting the adsorbed source material gas with a reductive gas thereby forming a Cu film (Refer to, for instance, JP 2004-6856A).
There has been known the use of a β-diketone complex or a derivative thereof as a source material (Refer to, for instance, JP 2003-138378A) in forming a Cu film by a CVD process. If a film is formed by a ALD process by using the β-diketone complex as a source material, since the vaporized β-diketone complex has low wettability to a base layer, aggregation of the β-diketone complex may occur when adsorbing it to the base layer. Furthermore, since the nuclear density of Cu is low in the early stage of film formation, a Cu film having a rough surface is formed. Therefore, it is difficult to form an extremely thin Cu film.
The reduction reaction with the use of a reductive gas takes a long time. Thus, it is desirable to shorten the reduction-step time for improving the total throughput of the entire film-forming process. However, if the reduction-step time is shortened, impurities such as carbon originated from the source material gas are generated on an interface between the base layer and the Cu film, and the Cu film is easily affected by oxidization of the base layer, and therefore the adhesion of the Cu film to the base layer becomes lower and the surface roughness of the film becomes disadvantageously remarkable. It is thus difficult to achieve both improvement of the throughput by shortening the reduction-step time and improvement of the film quality.